I like mixing Santa Cruz mango lemonade with club soda, or any lemonade with club soda, to make a sparkling lemonade. The mango is my favorite, though.
For me, I often drink mojitos without rum (heresy to some, I know); I just like the combination of club soda, mint, lime, and a bit of sugar.
Suffice it to say, club soda is a mainstay of our fridge.
One of our favorite places to eat in town serves a variety of mocktails that I've been meaning to attempt at home:
Frutta della Vallee: peach puree, cranberry juice, and tonic
Life's a Beach: Pineapple juice, OJ, orgeat (almond syrup), lime juice, club soda
Lime Ricardo: ginger ale, cranberry, and lime
They also make "dry" sodas with rhubarb and cucumber. If you like cucumber water, it's good